Add FAQ About store history (#49)

content/docs/faq.md

@@ -77,3 +77,30 @@ npm i --save-dev @babel/preset-env@7.14
 rm -rf node_modules package-lock.json
 npm install
 ```
+
+### 3. Store nodes only keep 30 days of messages by default, what if I need to keep messages permanently?
+
+Waku store protocol at this point does not provide a scalable solution to serve a large size archival data
+(as store nodes need to persist the entire history on their own local storage space),
+due to this, this protocol is more suitable for serving recent historical messages.
+
+Nevertheless, research on the scalability aspect has been done and documented in [here](https://github.com/vacp2p/research/milestone/8).
+
+Note that it is possible for operators to run their own store node and set a higher value than the default ones:
+
+`nwaku`:
+
+```
+--store-capacity    Maximum number of messages to keep in store. [=50000].
+```
+
+`go-waku`:
+
+```
+--store-days value      maximum number of days before a message is removed from the store (default: 30)
+--store-capacity value  maximum number of messages to store (default: 50000)
+```
+
+
+
+